The field of the disclosure relates generally to fluid transport systems and, more particularly, to systems and methods for controlling a fluid transport system.
As oil and gas fields in shallow waters diminish, producers are tapping offshore fields in deeper waters with oil installations that operate far below the surface of the sea. The typical production equipment for such subsea oil recovery and production include a wellhead valve, slug catcher, multiphase pump, separator, recirculation valve, and topside choke valve. A portion of this equipment is located in a subsea boosting station which pumps the oil up a pipeline riser to the topside choke valve. The output of an offshore field, received at the wellhead of the subsea boosting station, typically includes a combination of hydrocarbon oil, hydrocarbon gas, and water. This mixed flow, pumped by the multiphase pump, may cause flow instabilities, such as slugging. Slugging occurs when gas separates from a mixed flow to form bubbles. In a severe slugging flow pattern, large hydrocarbon gas bubbles will accumulate. Once the hydrocarbon gas bubbles accumulate with a pressure that exceeds the liquid hydrostatic head across the pipeline riser, the hydrocarbon bubbles will travel from the field and into the subsea boosting station as a slug. These slugs, which have a gas volume fraction exceeding the operating characteristics of the multiphase pump, may contribute to a reduction in the service life of the multiphase pump if allowed to reach the multiphase pump.
The subsea station may include passive protection equipment which facilitates protecting the multiphase pump from a reduction in service life due to slug flow. Passive equipment may include one or more slug catchers. Typically, a slug catcher is a vessel including a buffer volume to store slugs travelling through the fluid transport system. The subsea station may also include active protection equipment to mitigate slug flow and multiphase pump surge. Pump surge occurs when the velocity of the multiphase fluid changes rapidly or becomes unsteady. The active equipment may also control a gas volume fraction at the inlet of the multiphase pump. Passive equipment may be inadequate to fully protect the multiphase pump or be cost prohibitive to install, and active equipment typically requires a plurality of sensors included in the production equipment of the subsea station. These sensors are typically difficult to position and may experience a reduction in service life due to the subsea environment in which they are located. It is therefore necessary to avoid the use of sensors while providing for control of active protection equipment to mitigate slug flow and multiphase pump surge.